Malaria- it is not just a human disease
Our world is changing - too much and too fast. Species are moving into higher latitudes and altitudes, often carrying new infectious agents with them. As climate changes, vectors of infectious diseases such as mosquitoes, often find themselves in excellent breeding environmental conditions for extended periods of time. They thrive in these altered climatic conditions, and so do the diseases they carry. Many of these vectors infect wild populations of birds. Many aspects influence disease transmission in birds - evolutionary history of the species, whether it is a migratory or non-migratory species, whether it evolved in isolation (such as on an island) or the mainland (where it was exposed to many parasites), the presence and diversity of vectors (mosquitoes and other arthropods) in its habitat, the structure and composition of the forest it inhabits, and climatic variables that influence bird migration and vector breeding.
This broad intersection of bird ecology, infectious disease transmission, and climate change is an area of novel ongoing research being conducted by Dr. Farah Ishtiaq. Dr. Ishtiaq, a Wellcome Trust/India Alliance fellow at the Indian Institute of Science, Bangalore, is an ecologist and evolutionary biologist who uses field and lab based molecular techniques to understand infectious diseases in birds. The ultimate goal of her research is to determine how changes in temperature, the community of insect vectors, the migration patterns of birds, and changes in habitat affect the rate of parasite infection and its spread in high altitude areas that do not probably have blood parasites such as malaria.
“When we think about malaria, we immediately think of people in tropical areas being bitten by mosquitoes and getting infected with the disease. However, malarial parasites influence bird populations, but we don’t always make that connection”, says Dr. Ishtiaq. “Avian malaria is closely related to human malaria. But, unlike the human form, it is not strictly a tropical disease. It is found in many temperate birds”, she adds.
The risk and severity of infection depends on the evolutionary history of the species. If the species was not exposed to the parasite during its evolution, it may not have evolved the immunity to fight diseases and hence, infection may be more severe. A classic example of such a case is avian malaria in the Hawaiian archipelago. Species on this remote island system have evolved in isolation over millions of years, which has resulted in several endemic species not found anywhere else on earth. Populations of most species of honeycreepers, an endemic group of birds in the archipelago, have been severely impacted due to the introduction of non-Hawaiian species to the islands from different parts of the world during human occupation.
These introduced species of birds caused severe decline in the native populations of honeycreepers. The mechanism by which this happened is multidimensional: ecological - competing for limited resources, anthropogenic - hunting of native birds, and infectious diseases - introduction of novel parasites for which the species had not developed a defense mechanism, to name a few. Recent studies have shown that malarial infection in honeycreepers have caused populations at lower elevations to decline. The spread of infection to higher elevations has been higher due to changing climatic conditions. Populations at high elevations where the parasite cannot survive are still relatively free of infection, but changing temperature and rainfall regimes can accelerate the process.
Avian infectious diseases have not been well-researched in tropical areas. This is where Dr. Ishtiaq brings her expertise and draws on her experience of working on avian diseases across the world. Elevation gradients across the Himalayan range allows Dr. Ishtiaq to ask similar questions about the presence and evolution of infectious avian diseases that she previously worked on in Hawaii. However, the Himalayan system is more complicated since there are many species of blood parasites in comparison to Hawaii where only species of malaria Plasmodium relictum has been the pathogen. The plains along the Himalaya range - called the Terai, was once infamous for high rates of malaria infection until it was controlled through the use of DDT in 1950s. Species in the plains may have evolved with malaria and other blood parasites, but high-elevation residents may not have been exposed to the parasites during their evolutionary history. Therefore, much like the Hawaii example, there are species of birds that have differential exposure and evolutionary machinery to deal with parasites. One can then hypothesize that the resident high altitude species have low prevalence of the malarial parasite, the ones in the plains could be reservoirs of the parasites and the altitudinal migrants act as the bridge for parasites between their wintering and breeding grounds. A previous region-wide study conducted by Dr. Ishtiaq had suggested these patterns of higher prevalence of blood parasites at low altitudes and in native populations of birds in Asia. Her lab is now conducting more in-depth studies in the Western Himalaya to unravel and untangle these initial findings.
A day in Dr Ishtiaq’s lab could be spent mist-netting birds in the Himalaya, dissecting salivary glands of mosquitoes under a microscope, or running DNA from samples through a sequencing machine. She uses a combination of these cutting edge techniques and high-end computational and analytical methods to answer her research questions. “I like the fact that I’m not constantly in the lab processing samples. I love being outdoors in natural places teeming with wildlife. Having a field research component helps bring important perspective to my research”.
This research is the first effort in unravelling the complex interplay of climate, altitude, deforestation and infectious diseases of wild birds in a biodiversity rich region of the world undergoing rapid deforestation. Along with malaria causing Plasmodium, Dr. Ishtiaq is also studying other vector-borne blood parasites - Haemoproteus and Leucocytozoon in the Himalaya. By comparing the prevalence of parasites across gradients of elevation and deforestation, she is setting benchmarks to answer many questions about the evolution and ecology of infectious diseases in South Asia. “I plan to synthesize traditional and modern methodologies to make strides in answering fundamental questions that will impact biomedical research and conservation policy”, says Dr. Ishtiaq.
About the scientist
Dr Farah Ishtiaq is a wildlife ecologist and Wellcome Trust/DBT India Alliance Intermediate Fellow at the Centre for Ecological Sciences, Indian Institute of Science, Bangalore. Her research examines the effects of infectious diseases on the ecology and evolution of birds. To learn more about her work, visit her websites http://bio.iisc.ac.in/?q=faculty/farah-ishtiaqandhttp://wellcomebirdmalaria.weebly.com/research.html
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